RT9428

8

DS9428-01

October 2014

www.richtek.com

©

Copyright

2014 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

Application Information

Voltaic Gauge Theory and Performance

The embedded Fuel Gauge calculates and determines the

Li+ battery SOC according to battery voltage only.

The algorithm estimates the increasing or decreasing SOC

by an iteration model according to the difference between

battery voltage and the battery OCV. The dynamic voltaic

information can effectively emulate the Li+ battery behavior

and determines the SOC (%), but can't report capacity (mAh).

The calculation is based on the battery voltage information

and the dynamic difference between battery voltage and

relaxed OCV, by using iteration algorithm to estimate the

increasing or decreasing SOC to calculate SOC.

Comparing to coulomb counter based fuel gauge solution;

voltaic gauge does not accumulate error with time and

current. The coulomb counter based fuel gauge suffers

from SOC drift due to current-sense error and cell self-

discharge. Even there is a very small current sensing error,

the coulomb counter accumulates the error from time to

time. The accumulated error can be eliminated by only

full charged or full discharged. The VoltaicGauge

estimates battery SOC by only voltage information and

will not accumulate error because it does not rely on battery

current information.

Power On

When the IC is powered on by the battery insertion, the

IC measures the battery voltage quickly and predicts the

first SOC according to the voltage. The first SOC would

be accurate if the battery has been well relaxed for over

30 min. Otherwise, the initial SOC error occurs.

However, the initial SOC error will be convergent and the

SOC will be adjusted gradually and finally approach to the

accurate SOC without accumulation error.

Quick Sensing

A Quick Sensing operation allows the RT9428 to restart

sensing and SOC calculation. It has the same behavior

as power on. The operation is used to reduce the initial

SOC error caused by unwell power-on sequence. A Quick

Sensing operation could be performed by either a rising

the Control register.

Sleep Mode

RT9428 will enter sleep mode if host pulls low both SDA

and SCL to logic-low at least 2.5s. All operation such as

voltage measurement and SOC calculation are halted and

power consumption is reduced under 3

μA in sleep mode.

Any rising edge of SDA or SCL will transfer IC back to

active mode immediately.

The other way to enter sleep mode is write [Sleep] bit in

the Config register to 1 through I

the only way to exit sleep mode is to write [Sleep] bit to

logic 0 or power on reset the IC.

ALERT Interrupt

The RT9428 monitors the SOC and reports the alert

condition if the SOC change over 1% or if the SOC falls

below the SOCLow which is in the Config (0Dh) register.

When alert condition occurs, the RT9428 outputs logic-

low to the ALERT pin and sets 1 to the [Alert] bit in the

Config register and sets 1 to the corresponding alert flag

in the Status register. The only three ways to recover the

alert condition is writing 0 to clear [Alert] bit or writing 0 to

clear both [SL] and [SC] bit or power on reset. Before the

recovery, the [Alert] bit will keep 1 and the ALERT pin will

keep logic-low. It can’t recover the alert condition by

entering sleep mode.

Please note that the SOC low alert detection function is

enable when power on.

QS pin active high to restart the SOC calculation, and

pull low to GND during normal operation.

Temperature Compensation

To maximize the SOC performance, the host must

measure battery temperature periodically, and

compensate the VGCOMP Voltaic-Gauge parameter at

least once per minute.

Contact Richtek for instructions for temperature

compensation.